An MRAM is a memory using a magnetic material for a memory element and storing data by a direction of magnetization of the magnetic material, that is, a memory retaining data by storing information in a spin of an electron, and has a circuit configured to be capable of random access. One of the memory element utilized for the MRAM is an MTJ element. Note that the present specification uses “MTJ element” as a concept including a TMR (Tunneling Magneto-Resistance) element.
A memory cell part of the MRAM is provided with a bottom electrode, a bottom magnetic film laminated over a part of the bottom electrode, a tunnel insulating film laminated over the bottom magnetic film, a top magnetic film laminated over the tunnel insulating film, a top electrode laminated over the top magnetic film, and a protection film formed over the bottom electrode so as to cover this laminated structure. Note that the MTJ element is composed of the above bottom magnetic film, tunnel insulating film, and top magnetic film.
Conventionally, Ta, Ti, or Cu, for example, has been used for the above bottom electrode and a nitride film or alumina, for example, has been used for the above protection film. As a prior art regarding such an MTJ element structure, Patent document 1 (Japanese patent laid-open No. 2007-158301) is known, for example.